This invention relates generally to xerographic copying or reproduction apparatus and, more particularly, to a contact fusing system for fixing electroscopic toner material to a support member.
In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual image can be either fixed directly upon the photosensitive member or transferred from the member to a sheet of plain paper with subsequent affixing of the image thereto.
In order to permanently affix or fuse electroscopic toner material onto a support member by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This action cuases the toner to be absorbed to some extent into the fibers of the support member which, in many instances constitutes plain paper. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be firmly bonded to the support member. In both the xerographic as well as the electrophotographic recording arts, the use of thermal energy for fixing toner images onto a support member is old and well known.
One approach to thermal fusing of electroscopic toner images onto a support has been to pass the support with the toner images thereon between a pair of opposed roller members, at least one of which is heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip.
One type of roll fuser comprises a conformable outer layer such as silicone rubber. In order to optimize the life expectancy of such a construction and insure satisfactory release of coalesced toner carried by the substrate it should be operated at a relatively low temperature (i.e. 300.degree. F. ). However, where only a single fuser (prior art systems are known which employ plural fusers, for example, as disclosed in U.S. Pat. No. 3,861,863) has been provided it has been necessary to operate such fuser rolls at substantially higher temperatures (i.e. 380.degree.-400.degree. F.) in order to adequately fuse thick or high density images.
Accordingly, it is the primary object of this invention to provide new and improved fusers for use in an electrophotographic copying apparatus.
It is a more particular object of this invention to provide an improved roll fuser capable of operating at a lower temperature yet capable of satisfactory fusing low and high density images.